In hygiene products, such as diapers, sanitary napkins and incontinence pads, absorption bodies or absorption cores of so-called fluff are used. Fluff is made by dry defibering of cellulose pulp in form of long webs in rolls or sheets in bundles. To reduce the defibration energy and facilitate the defibering the pulp is provided before or on the wet machine with certain additives, which reduce the formation of bonds and lowers the friction between the fibers in the pulp. For example, for this purpose cationic tensides that have good adherence to the fibers are used, see e.g. U.S. Pat. No. 3,930,933. To reduce the negative effect of the tensides on the liquid absorption properties of the pulp and also on its brightness, the cationic tensides are often combined with e.g. nonionic tensides.
In resent years, an increased use of so-called synthetic superabsorbents has resulted in that the amount of cellulose fluff used in certain hygiene products has been radically reduced. These superabsorbents do not contribute to the integrity in the absorption pad and therefore it has become more and more important that the included cellulose fibers can contribute to the strength in the absorption cores of the hygiene products. Therefore, the so-called network strength of the cellulose fluff has become an even more preferred property. A good network strength is generally obtained if, in the process where the fluff pulp is dry defibered, an effective defibering or alternatively disintegration of fiber is achieved. Consequently, low so-called knot content is aimed at. Even though addition of softening organic tensides of cationic and nonionic type according to prior art yield a considerably improved defibering, they have a detrimental effect on the absorption properties of the fluff pulp.
In the patent SE 508 898 (Stora) is described a method of making a cellulose pulp by treatment with a non-polymeric aluminium salt. This treatment is said to improve the defibering properties of a fluff pulp.
For the purpose of obtaining in absorption products improved absorption in fluff pulp, the patent SE 500 858 (SCA) describes a method of producing fibers with increased specific surface by adhering hydrophilic chemicals consisting of positive inorganic ions in the form of different types of inorganic salts onto the fiber surface. There is i.a. mentioned aluminium as an example of positive inorganic ions, and as an example of an inorganic salt i.a. calcium carbonate is mentioned. The patent is directed to the positive effect that can be obtained on the absorption rate due to the increased specific surface. Thus, nothing is mentioned about the effects on defibering.
In WO 98/17856 is described a method of making a readily defibered cellulose pulp for use in absorbent products based on cellulose fluff. According to the description the method is based on that noncellulosic particles are added to the cellulose pulp together with a retention aid when the pulp is in an aqueous suspension. According to the claims so-called mineral fillers of e.g. clay, calcium carbonate or talc are used. A typical added amount is said to be 1-30% of the weight of the final cellulose product. In the application WO 98/17856 there are mentioned effects on defibration energy, knot content, absorption properties etc, but no effects on the network strength, which is an important property of the mechanical coherence of the absorbent products, have been presented.
The above mentioned methods with alum and calcium carbonate, respectively, according to SE 500 858 may have drawbacks due to limitations of the pH-intervals at which they are suitable. The complex equilibriums for the aluminium hydroxide systems lead to an optimum in the interval of pH 5.5-6.5. The method with calcium carbonate is used most advantageously at a pH above 7. Since both alum and carbonate, when they are in dry state in a final absorption product, can be affected by and partly dissolved by added liquid, unwanted effects of the dissolved chemicals may be obtained. It can be mentioned that the pH level in extracts, and possible interaction between the products and the skin, may be affected. From an end-user's point of view it may thus be an advantage if the desired effects can be obtained with a more inert additive than alum or calcium carbonate.
An addition of an inert component in the making of fluff pulp would also result in that the pH level in the pulp stock would not be critical. Any extra additives in the form of alkali or acid to adjust the pH would then not be needed.